Committee chair Mark Drakeford AM said: "We are also concerned that assessment methods are not just inconsistent across local health boards in Wales but can be inconsistent across different departments within the same hospital."

The reports calls for all hospitals to make sure doctors stick to the guidelines and that tackling the problem should should be a top priority.

The findings were welcomed by Dr Simon Noble, medical director for Wales for Lifeblood: The Thrombosis Charity.

He said the figure of 900 preventable deaths was "likely to be an underestimate" because "we are often very poor at picking up blood clots as a cause of death".

Dr Noble added: "The benefits of preventing a hospital-acquired thrombosis is supported by a wealth of evidence.

"Trials involving thousands of patients have been conducted and have shown that this is not only highly effective but will save the health service money.

"It makes sense in health terms and in economic terms. It saves lives and it saves money."

Dr Noble declined to put a figure on the number of preventable hospital-acquired thrombosis deaths in Wales but said a 2005 Commons report which estimated there were 25,000 across the UK annually suggested Wales' element of that statistic would be around 1,700.

'Devastating condition'

He added: "Patients go in to hospital to be cured. They don't go in to hospital and expect to pick up a life-threatening condition."

A Welsh government spokeswoman said: "We recognise Venous Thromboembolism Prevention (VTE) is a devastating condition and are committed to reducing its incidence across Wales.

"The National Institute for Health and Clinical Excellence (NICE) guidance should be used to ensure patients are receiving the most appropriate care.

"The guidance does not, however, override the individual responsibility of healthcare professionals to make decisions appropriate to the circumstances of the individual patient."